Activity

Definition of Activity

Definition Last Updated 17-Dec-2015 12:51

Activity is continuous change in one or more observables during a specified period of time, which, if the activity is current, is open-ended to the future and may be open-ended in the past; an entity engaged in activity has that activity as a behaviour is an performer.

An activity is recognised pattern of change, i.e. a mapping from particular initial states to particular outcomes, which may or may not be goals.

Discussion

Activity vs. Behaviour

All behaviour is activity, but not all activities are behaviours: behaviour requires the identification of an entity to which the activity can be attributed; activity does not.

Examples:

“The lioness is creeping through the long grass.” describes a behaviour: the lioness is attributed the activity

“Some of the long grass is waving.” describes an activity: some grass is not an entity to which the activity can be attributed

“There is movement in the long grass.” is ambiguous: “in” suggests that only part of the long grass is moving, but it is not well-identified enough to be an entity; but, if the emphasis were on “the long grass”, suggesting a defined border separating long grass from shorter grass, the long grass might be in fact be an entity in its own right1If this type of ambiguity (not some actual threatening movement in long grass somewhere) turns out to be a significant problem for anybody I would a) be surprised b) like to know about it. .

An Activity

Note that the performer engaged in an activity need not be aware of or even capable of recognising the initial states or outcomes that define an activity: activity may just happen.

Is Waiting an Activity – or the Absence of Activity?

Waiting is an activity because waiting for something entails continuous observation in order to determine when that something (the state of interest) occurs. Even if an observer only observes intermittently, it must still monitor the passage of time in order to determine when to make an observation. Waiting for something also implies an expectation or belief – whether that justified or not – that that that something will occur.

According to the definition given here, when a performer does not engage in a particular activity, or perform a particular action until caused to do so by some external event, the performer is simply not doing a particular thing, the performer is not necessarily inactive: the performer may be doing something else.

When, for example, a piece of hardware or software is said to be waiting for input it may be:

Polling (repeatedly observing) the input channel as fast as possible (e.g. in a tight causal loop) or it may be

Polling a timer prior to checking the input channel at particular intervals

Inactive until triggered into activity by a specific signal such as an interrupt